The present invention is directed, in general, to wireless communication systems and methods of operating the same, and, in particular, to narrowband communication systems for one-way and two-way transmission of voice and data messages.
The demand for better and cheaper wireless telecommunication services and equipment continues to grow at a rapid pace. Much of this growth is spurred by the Federal Communication Commission""s (xe2x80x9cFCCxe2x80x9d) approval of certain frequency bands for the next generation of Personal Communication Service (xe2x80x9cPCSxe2x80x9d) devices that provide voice telephone service as well as advanced voice and/or data message paging services. A relatively small portion of the available spectrum was set aside for narrowband PCS, which is more suited to advanced message paging services, to encourage efficient use of the available spectrum.
There are a number of well-known wireless communication techniques that attempt to maximize the efficiency with which the available spectrum is used. These methods include frequency division multiple access (xe2x80x9cFDMAxe2x80x9d), time division multiple access (xe2x80x9cTDMAxe2x80x9d), code division multiple access (xe2x80x9cCDMAxe2x80x9d), and the like. The term xe2x80x9cmultiple accessxe2x80x9d means that multiple, simultaneous users (or xe2x80x9csubscribersxe2x80x9d) are supported in each of these systems.
In an FDMA system, for instance, the total available radio spectrum is divided into separate frequency bands (or xe2x80x9cchannelsxe2x80x9d) of, for example, 25-30 KHz for those systems based on the xe2x80x9cAMPSxe2x80x9d or xe2x80x9cTACSxe2x80x9d standards, or 10 KHz for newer systems, such the narrowband PCS (xe2x80x9cNPCSxe2x80x9d) advanced messaging systems. In FDMA, only one subscriber at a time is assigned to a channel. No other subscriber may access this channel until the transmission of the message sent by the first subscriber is completed.
In a TDMA system, the total available radio spectrum is again divided into separate frequency bands. Each band is then temporally subdivided into, for example, three time slots. Only one subscriber at a time is assigned to each channel, where a channel corresponds to a particular frequency band and a particular time slot for that band. No other subscriber may access this channel until the transmission of the message sent by the first subscriber is completed.
In a CDMA system, the total available radio spectrum is used by each subscriber. Each subscriber transmits a unique, pseudo-random noise (xe2x80x9cPNxe2x80x9d) code sequence as a spread spectrum signal. The subscriber""s transmitter and the receiving base station share the code, which is used to distinguish the subscriber from other subscribers in the system, who use different codes PN codes. Thus, a CDMA system uses codes rather than frequency and/or time slots to provide multiple access.
The total capacity of a multiple access system may be further improved by dividing a wireless system into cells and, in the case of FDMA and TDMA, using only different frequency channels in adjoining cells. The organization of message paging and cellular telephone systems into cells is widely known and understood. Division into cells is accomplished by limiting the transmission range of both the base stations and the mobile communication units. The frequencies used in one cell do not interfere with the different frequencies used in the adjoining cells and are not transmitted far enough to interfere with identical frequencies used in more remote, non-adjoining cells. Frequency xe2x80x9creusexe2x80x9d is therefore possible by dividing a TDMA or FDMA system into cells.
In the case of CDMA, division of the system into cells does not affect frequency allocation, since all subscribers use the same amount of spectrum. However, there are less subscribers per cell in smaller cells, so there is less interference to distort the signal transmitted by each subscriber. Thus, capacity is still improved for the overall system.
The structure of a message paging system is somewhat different than cellular telephone systems. In a message paging system, all of the base station transmitters throughout a wide coverage area are synchronized and simultaneously broadcast (i.e., simulcast) a paging message in a forward-channel to a subscriber""s pager. This simulcast increases the likelihood that the paging message will reach the pager even through obstacles, such as buildings. The paging system does not assign the subscriber to a cell and transmit to the subscriber only in that cell, as in the case of a cellular telephone system.
However, even in a paging environment, there is a breakdown of the message paging system into cells. That is, due to the low power of a hand-held two-way pager, a message transmitted by a user in a reverse-channel has a very limited range compared to the base station transmitters. Therefore, a relatively large number of base station receivers must be deployed throughout the message paging system coverage area in order to ensure that the signal transmitted by any pager is received by a base station receiver. As a result, minimizing the number of receivers necessary to monitor the coverage area of a message paging system becomes an important consideration. Using less receivers lowers the infrastructure cost and, therefore, lowers the service cost to subscribers.
There exists a need in the art for an improved wireless communication system that minimizes the equipment cost necessary to operate the system. In particular, there is a need for an improved wireless messaging system that minimizes the number of base station receivers required to operate the system. There is a further need in the art for an improved narrowband messaging system capable of providing advanced two-way messaging services that maximizes frequency reuse and spectral efficiency with a minimum number of base station receivers.
The limitations inherent in the prior art described above are overcome by an improved base station for communicating with mobile communication units (e.g., message pagers, PCS devices, personal data assistant and other processing systems that include wireless communication functionality) in a wireless messaging system. In an advantageous embodiment, the base station includes: 1) a transmitter that is capable of transmitting messages to the communication units in a forward-channel having a first frequency range; 2) a receiver that is capable of receiving messages from the communication units in a reverse-channel having a second frequency range; and 3) an antenna that is capable of transmitting the forward-channel messages at a first angle of electrical downtilt below the horizon and receiving the reverse-channel messages at a second angle of electrical downtilt, wherein the second angle of electrical downtilt is less than the first angle of electrical downtilt.
According to an advantageous embodiment, the first angle of electrical downtilt is determined by the first frequency range and the second angle of electrical downtilt is determined by the second frequency range. As will be discussed in detail herebelow, the downtilt angle of a receive beam is preferably slightly below the horizon. Use of a relatively small angle of electrical downtilt in the reverse-channel allows the antenna to focus on signals from more distant communication units, including those beyond the boundaries of the coverage area in which the base station resides. This tends to increase the probability that the antenna will receive reverse-channel signals from communication units in other coverage areas, thereby increasing the overall macro-diversity of the antenna in the messaging network.
In an alternate embodiment of the present invention, the base station further comprises an amplifier disposed proximate the antenna for amplifying messages received in the reverse-channel prior to processing in the receiver. In a related embodiment, the antenna is a sectored antenna that is operable to transmit a forward-channel message in a selected direction at greater signal strength relative to a signal strength transmitted in a non-selected direction. In another related embodiment, the antenna is a sectored antenna operable to amplify a reverse-channel message received from a selected direction and attenuate a reverse-channel message received from a non-selected direction.
In another alternate embodiment of the present invention, the second angle of electrical downtilt is approximately zero degrees, such that the antenna is optimized to receive reverse-channel messages from remote communication units.
The foregoing SUMMARY OF THE INVENTION outlines, rather broadly, some advantageous features of various embodiments of the present invention so that those of ordinary skill in the art may better understand the DETAILED DESCRIPTION that follows. Additional features of the invention will be described hereafter that form the subject matter of the CLAIMS OF THE INVENTION. Those of ordinary skill in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes of god the present invention. Those of ordinary skill in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, be a property of, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.